1. Field of the Invention
The present invention relates to a fan system having improved availability, e.g., of the type used for supporting cooling of internal combustion engines, as well as a method for its operation.
2. Description of Related Art
It is generally customary to use electrical drives for cooling blowers on internal combustion engines. These electrical drives are operated via motor control modules (FCM or fan control module). A changeable pulse width modulated voltage (PWM) having a variable pulse duty factor (TV) is used to change the actual voltage present at an electrical drive developed as a DC motor, so that the rotational speed of the electrical drive is able to be influenced in this manner.
It is known that one may construct the motor control modules based on power semiconductors. These power semiconductors, and additional components required for their operation, have a power loss that is a function of the clock pulse of the voltage present or the pulse duty factor and the height of the voltage present. It is customary, for this reason, to monitor the temperature of the board on which the components mentioned are located, and to take measures to avoid critical heating of the board and the components located on it. For this purpose, temperature sensors are commonly used. It is known that as temperature sensors, one may use components that have a negative temperature coefficient, so-called NTC elements (negative temperature coefficient).
Among the measures used for avoiding critical temperatures in the area of the board of a motor control module, one that is well known is the monitoring of the board temperature and switching off the drive of the cooling blower when a critical temperature is exceeded. This creates thermal coupling between the temperature sensor and the power components on the board, which has the result that, upon the attainment of the critical temperature, for example, the drive of the blower is no longer available for any further supporting cooling of the coolant circuit of an internal combustion engine.
In connection with the blower system, it is also known that one may control the power semiconductors and the additional electronic components required for their operation, that are used in motor control modules, in such a way that operating points are avoided which have been proven to be connected with a maximum power loss at the respective component. Various semiconductor components based on transistors, used as switches, for example, show a strong dependence of the power loss on a present pulse duty factor of the control voltage, which has the result that, at typical switching frequencies required for the operation of fan motors, the power loss at such semiconductor components becomes a maximum when the pulse duty factor is approximately 99% of the maximum pulse duty factor that may be called for, that is, barely below continuous operation. Capacitors connected in parallel to power semiconductor elements frequently demonstrate a fundamentally different dependence of the power loss on the pulse duty factor with which the respective power semiconductors element is controlled. These capacitors frequently demonstrate a maximum power loss at a pulse duty factor of approximately 80% of the maximum pulse duty factor that may be called for. The behavior of these components is taken into account in the control of the circuit breakers in combination with the monitoring of the board temperature. When a board temperature is reached that is classified as being critical, the pulse duty factor is set to a constant value that ensures that critical pulse duty factors at increased power loss at the respective components is avoided until the board temperature has possibly reached non-critical values again. Only if this measure does not achieve success, there takes place, as in usual motor control modules, the complete switching off of the blower until the board has again reached temperature ranges in which the power electronics system is ready for operation. The setting of a constant pulse duty factor leads to the availability of the blower not being totally lost, but in a certain temperature window, no further regulated request for fan performance is able to take place. When there is an additional increase in the temperature, a complete shut-down of the availability of the blower also takes place (see, e.g., published European patent document EP 1383232A2).